HDPE, additives Pigments

Polyolefins are produced in a variety of forms HDPE and PP are produced as powders, while LDPE emerges from the melt preferably in the form of lenticular granules. All types, however, are supplied primarily as granules. As a rule, any thermoplastic transformation of a polymer powder to a granulate is carried out in the presence of additives. This is also partly true for pigments. 

Alpla Technik produced bottles with a density as low as 0.68 g/cm in developmental work. Addition of pigment slightly increases the density. The foam cells cannot be seen with the naked eye, but are visible with a microscope. The cell diameter is between 50 and 100 microns in the bottle neck and base, and about 30 microns in the walls where the polymer is stretched. The surface layer is solid HDPE, with microbubbles in the core. Two-layer versions of the bottle have a smoother bottle surface but are somewhat heavier than monolayer bottles. 

The HDPE, LDPE, and LLDPE can be stabilized by UV absorbers of type benzophenone or benzotriazole and also combination of HALS and UV-absorbers. Usually pipes used in irrigation are pigmented with white titanium dioxide or carbon black. Titanium dioxide may be used up to an additional level of 0.5 wt%. Each of the HALS and UV absorber may be added up to 0.05 wt% [50-53]. 

As mentioned previously, the most important pigment additive employed for light stability purposes is carbon black. The addition of 2% by weight of a well-dispersed carbon black of fine particle size should extend the outdoor life of most low- and HDPE to as much as 20 years in temperate climates, while even the addition of 0.2% should give 10 years ... 

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